The present invention relates to a method for processing an exposed silver halide color photographic material by a sequence of development, bleaching and fixing (such a process is hereunder also referred to as color photographic processing). More particularly, the invention relates to a color photographic processing method that can be completed in a shortened period of time by accelerated bleaching action. Specifically, the invention relates to a bleaching process capable of providing a color photographic image of good quality by performing consistent and adequate bleaching over an extended period of time with minimum deterioration with the elapse of time in performance.
The two basic steps of the processing of silver halide color photographic materials are color development and desilvering. In the color development step, the silver halide in the exposed silver halide photographic material is reduced by a color developing agent to form silver and the oxidized color developing agent reacts with a coupler to provide a dye image. Thereafter, the color photographic material enters the desilvering step wherein by the action of certain types oxidizing agent (conventionally referred to as a bleaching agent), the silver formed in the development step is oxidized and eliminated from the photographic material by being dissolved with a silver ion complexing agent conventionally referred to as a fixing agent. As a result, the final image formed in the photographic material is a dye image. The actual photographic process involves, in addition to the two basic steps of color development and desilvering, auxiliary steps performed either for the purpose of maintaining the desired photographic and physical properties of the image or for the purpose of improving the archival quality of the image. Among the solutions used in auxiliary steps are a hardening bath used to prevent excessive softening of the light-sensitive layer during processing, a stopping bath that effectively stops the development reaction, an image stabilizing bath that stabilizes the image, and a defilming bath for removing the backing layer from the support.
The desilvering step is carried out either in a single stage using a bleach-fix bath containing both a bleaching agent and a fixing agent (conventionally referred to as a "blix" bath) or in two stages using both a bleaching bath and a fixing bath.
Oxidizing agents conventionally incorporated in the bleaching solution are potassium ferricyanide, potassium bichromate, iron (III) complex salts and persulfate salts. The solution using potassium ferricyanide exhibits excellent bleaching action, but ferricyanide ions or ferrocyanide ions in their reduced form are discharged in the form of an overflow during processing or a carryover into rinsing water after the bleaching and may sometimes experience photochemical oxidation to form cyanide compounds. The cyanide compounds are highly toxic and present a great hazard. Therefore, it is desired to develop bleaching agents that can be used in place of potassium ferricyanide.
Iron (III) complex salts are sometimes used as a bleaching agent in a bleach-fix solution intended for the processing of color photographic papers (see German Pat. Nos. 866,605 and 966410; British Pat. Nos. 746,567, 933,088 and 1,014,396). However, bleach-fixing agents containing the iron (III) complex salts are weak in oxidizing power and are not suitable for use in the processing of picture taking color photographic materials having high concentrations of silver halide and using silver iodobromide. Therefore, it is desired to increase the oxidizing power of bleaching solutions and bleach-fixing solutions using iron (III) complex salts.
Iron (III) complex salts may be used together with bromide salt. However, as in the case of the bleach-fixing solution, a bleaching bath containing iron (III) complex salts has a weak oxidizing power and takes an undesirably long period for completing the bleaching.
Another compounds known to be usable as bleaching agents are persulfate salts. A persulfate salt usually makes up a bleaching agent together with a chloride. However, one great defect with the bleaching bath containing a persulfate salt is that it has a still weaker oxidizing power than the one containing an iron (III) complex salt, and hence requires an extremely long time to complete the bleaching.
Bleaching accelerators are used in order to effect satisfactory bleaching or bleach-fixing with these bleaching or bleach-fixing solutions having weak bleaching power. Accelerators known for use with bleaching solution containing an iron (III) complex salt and those for use with the bleach-fixing solution containing both the iron (III) complex salt and thiosulfate include thiols such as aminoalkylene thiol, thioglycerin and cysteine, as well as disulfides such as cystine and cystamine (see U.S. Pat. No. 3,893,858).
Of these accelerators, aminoalkyl-one thiol is the most effective, but this compound is strongly malodorous and is not suitable for independent use. This problem can be solved by using a thiol precursor that is not malodorous and which releases thiol in the processing bath.
A method is known for increasing the effectiveness of a persulfate containing bleaching bath by adding a thio compound to either the bleaching bath or any one of the bath that are used after development up to the stage of bleaching (see Research Disclosure, No. 15704, May 1977). This publication lists as accelerating compounds aminoalkylene thiols (e.g. 2-aminoethane thiol, 3-aminopropane thiol, 2-dimethylaminoethane thiol, 3-dimethylaminopropane thiol, N-methyl-N-ethyl-aminoethane thiol and 2-diethylaminoethane thiol) and thiol precursors such as disulfide and isothiuronium salts. However, not all of these compounds have satisfactory accelerating effect, and many of them exhibit the desired accelerating effect for some time after the preparation of the processing solution, but their effect is significantly decreased after the solution is used to process photographic materials or after the solution is stored for some period. In order to solve this practical problem, an increased amount of the accelerator is incorporated in the processing solution, or alternatively, an increased amount of the accelerator is used in a replenisher for maintaining the effectiveness of the accelerator.